Hitherto, “Failure Detecting Device for AC Motor Control Circuit” for example, disclosed in patent document 1 is named as a break detector of a motor.
FIG. 3 is a system configuration diagram of an AC motor control circuit known in JP-A-9-172791 for detecting an anomaly of a current sensor, etc., in a circuit for supplying power from a battery 112 to a three-phase AC motor 110.
In the figure, a controller 116 for controlling the operation of an IPM 114 contains a CPU 118, ROM 120, RAM 122, an I/O port 124, and an A/D converter 126, the ROM 120 stores a control program to be executed by the CPU 118, fixed parameters, etc., and the RAM 122 provides a work area for the CPU 118. The I/O port 124 and the A/D converter 126 are each means for inputting external digital or analog information. Here, the torque command value indicating the torque to be output from the motor 110 and output of a resolver 128 added to the motor 110 for generating a signal in response to rotation of a rotator of the motor are input from the I/O port 124. The A/D converter 126 converts outputs ius, ivs, and iws of current sensors 130u, 130v, and 130w provided corresponding to the three phases of the motor 110 from analog form into digital form for input to the controller 116.
The CPU 118 supplies a control signal to the IPM 114 so that the torque corresponding to the torque command value is output from the motor 110. At the time, the CPU 118 detects the output signal of the resolver 128 (the number of revolutions or the rotation angle) and the outputs ius, ivs, and iws of the current sensors 130u, 130v, and 130w (phase current instantaneous values) and when the CPU 118 makes a transition to an anomaly detection routine during usual operation control, the CPU 118 finds estimated values of phase currents, iuc, ivc, and iwc, from phase voltage command values and makes a comparison between deviation from the phase output current value ius, ivs, iws, |iuc-ius|, |ivc-ivs|, |iwc-iws|, and threshold value ΔI1u, ΔI1v, ΔI1w for determining an anomaly.
Another inspection device is “Motor Controller” disclosed in JP-A-5-137380. FIG. 4 is a circuit diagram thereof. A control circuit 207a controls a drive circuit 205 and operates upon reception of a motor start command 210 and before a motor is started, gives a break detection command 213 to a break detection circuit 212 and checks whether or not circuit is abnormal according to an overcurrent detection signal. If no anomaly is detected, the control circuit starts a motor 201; if an anomaly is detected, the control circuit stops starting the motor 201. In this case, a break detection signal 214 of the break detection circuit 212 is provided for conducting an energization test of each phase by applying a direct current; in the energized phase, an uncontrolled direct current flows unless an anomaly exists in the path, and thus an overcurrent state is entered and this fact is used to detect an overcurrent.
In the related art described above, however, a motor break cannot directly be detected and a speed detection value does not follow a speed command value due to a motor break and consequently the torque command becomes a large value. As the torque command value continues to take a large value, it is detected as an overload alarm and thus for the anomaly detection shown in the patent document, the delay time in the anomaly detection during the operation is large and the moving part of a machine incorporating a motor may run away, causing damage to the machine; this is a problem.
Since a break in a power line cannot rapidly be detected before the operation, if the motor power line for driving a vertical axis is broken, a workpiece drops after a mechanical brake is released; this is also a problem.
It is therefore an object of a first aspect of the invention to provide a motor power line break detection method of an AC servo driver capable of immediately detecting the presence or absence of a break in a motor power line during the operation and stopping a machine with safety before causing damage to the machine.
Further, it is an object of a second aspect of the invention to provide a motor power line break detection method of an AC servo driver capable of detecting the presence or absence of a break in a motor power line with safety while a mechanical brake is held before the operation and preventing a workpiece from dropping without releasing the mechanical brake if a break is detected.